Mr Livingstone said much of the cost would be recouped

He was asked about conflicting remarks from the mayor and Culture Secretary Tessa Jowell on the projected budget.

Ms Jowell told MPs on Tuesday the estimated �2.4bn bill for the Olympic Park had risen �900m to �3.3bn.

Mr Livingstone later said she had "made a mistake" and insisted the Olympic Park bill was still �2.4bn.

'Clarify the position'

He said any extra costs were to do with infrastructure for new homes - contradicting Ms Jowell's statement that the �900m was separate from regeneration.

Mr Livingstone also said Ms Jowell had failed to take into account other changes to the plan which had cut back the overall bill.

On Thursday shadow Commons leader Theresa May said a statement to MPs on the budget and the project's current status was needed to "clarify the position and clear up the confusion".

Ken can write as many blank cheques as he wants, the thing is they won't be banked or paid Jack Straw Commons leader Q&A: Olympics costs

She told MPs London's winning Olympic bid had been a wonderful coup which would leave a lasting legacy.

But she said it was not an excuse for a "blank cheque", signed by Mr Livingstone and paid for by the lottery and council tax payers.

Mr Straw told MPs that Mr Livingstone might be painting a different picture but "what I say is the truth".

He said Ms Jowell was right to publish the detailed figures, in order that a judgement could be made.

Rising costs

"Ken can write as many blank cheques as he wants, the thing is they won't be banked or paid because it is a matter for the government to decide," he added.

The government made the decisions about the overall cost, because it had decided from the outset that it had to stand behind the bid, Mr Straw said.

He added that ministers were being "very assiduous" about bearing down on costs.

The cost of building the Olympic Park has risen �900m

And while it was right to be worried about rising costs, Britain was two years further ahead than either Athens or Sydney had been at the equivalent time, he said.

There has been speculation that the overall cost of the Games could rocket to �8bn - although the government has said it "does not recognise" that figure.

Ms Jowell restricted her estimate of the rise to the Olympic Park, admitting that other costs - like anticipated extra security - had yet to be worked out.

A row over the size of a contingency fund and an unexpected VAT bill have also not yet been resolved.

The Olympic Park is being funded publicly, through a �20-a-year surcharge on each of London's council tax payers for 12 years and the National Lottery.

Regeneration is being funded through central government, while staging the Games is being privately funded.

Both the Liberal Democrats and the Conservatives have said Parliament needs to scrutinise the costs - which they expect to rise further.